The present invention relates to friction materials suitable for use in braking members, e.g., clutch facings and braking elements, incorporated in braking devices as for automobiles, aircrafts, railway vehicles and industrial apparatuses.
Friction materials as heretofore used to form braking members utilize asbestos dispersed in and integrated by organic or inorganic binders. However, such friction materials have suffered from insufficient friction and abrasion properties. Also, asbestos is a cancer-causing substance and presents an environmental hygienic problem. Under these circumstances, it has been strongly demanded to develop asbestos substitutes.
In response to such demands, friction materials have been proposed which utilize potassium titanate fibers as base fibers or a friction control agent. The potassium titanate fiber is non-carcinogenic, unlike asbestos, shows good heat resistance and is effective in preventing a fading phenomenon and stabilizing friction properties against heat.
However, the incorporation of potassium titanate fibers in friction materials has not yet presented a sufficient solution to xe2x80x9cbraking noisexe2x80x9d developed in braking devices.
Also, the potassium titanate fibers, because of their fibrous form, have a greater bulk and a lower degree of fluidity, leading to their tendency to deposit on a wall of a feed passage and block the passage during the manufacture of friction materials, which has been a problem.
The present invention is directed toward solving the above-described problems and its object is to provide a friction material which exhibits excellent friction and abrasion properties and is highly productive.
The friction material of the present invention is characterized as containing, as a friction control agent, 3-50% by weight of one or more substances selected from flat layered titanates represented by the general formula (1), AxMyTi2xe2x88x92yO4 (wherein A represents an alkaline metal other than lithium; M represents one or more elements selected from lithium, magnesium, zinc, nickel, copper, iron, aluminum, gallium and manganese; x is a number of 0.5-1.0; and y is a number of 0.25-1.0) and flat layered titanic acids represented by the general formula (2), Hx(Mxe2x80x2y)zTi2xe2x88x92yO4.nH2O (wherein Mxe2x80x2 represents one or more elements selected from lithium, magnesium, zinc, nickel, copper, iron, aluminum, gallium and manganese; x is a number of 0.5-1.0; y is a number of 0.25-1.0; z is a number of 0 or 1; and n is a number of 0xe2x89xa6nxe2x89xa62). Specifically, A may be sodium, potassium, rubidium or cesium, for example.
The substances for use as a friction control agent in the present invention, i.e., the flat layered titanates and titanic acids as respectively represented by the general formulas (1) and (2) have friction and abrasion properties better stabilized against temperature change, which make them particularly suitable for use as a friction control agent incorporated in friction materials. Due to their non-fibrous form, contrary to potassium titanate fibers, they are unlikely to block a feed passage during a manufacturing process. Also, due to the absence of respirable fibers, a working environment is unlikely to be adversely affected.
The friction material of the present invention, because of its inclusion of a flat layered titanate and/or a titanic acid as a friction control agent, have the following functions and effects.
(1) The friction and abrasion properties are stabilized because of the flat layered structure of the friction control agent.
(2) The strength of friction materials is improved as a result of the higher aspect ratio of the friction control agent.
(3) The preparation of a raw material mixture is facilitated by the increased fluidity of the friction control agent.
(4) A working environment is kept in a clean condition because the production of respirable dusts is maintained at a very low degree of occurrence.
(5) A friction coefficient is kept stable over a wide temperature range from low to high temperature because of the increased heat resistance.